The recovery and isolation of radionuclides from environmental and bioassay samples is complicated by the presence of silica, aluminum and iron (III) as well as other frequently present ions such as titanium, bismuth and phosphate. The isolation of the actinides, lanthanides and radium from such samples in the past has involved time-consuming, expensive and sometimes hazardous procedures.
A number of previously described procedures for the determination of the actinide plutonium (Pu) in urine, for example, involved preconcentration of small amounts of Pu from the vast excess of matrix substances present in urine samples by precipitation reactions, adsorption on glass fiber, extraction, extraction chromatography or ion exchange. Of these, precipitation reactions appear to provide the most satisfactory results. However, such methods are complex, time consuming and relatively expensive.
U.S. Pat. No. 4,548,790 dated Oct. 22, 1985 describes a group of neutral bifunctional organophosphorus compounds broadly described as alkyl(phenyl)-N,N-dialkyl-carbamoylmethylphosphine oxides (hereinafter referred to as CMPO) that are useful for the recovery of actinide and lanthanide values from acidic solutions containing these and other metal values. The combination of the CMPO extractants with a phase modifier such as tri-n-butyl phosphate in a normal paraffin hydrocarbon diluent is described in U.S. Pat. No. 4,574,072. U.S. Pat. No. 4,835,107 describes passing samples in a mineral acid solution through a separation column of an alkyl(phenyl)-N,N-dialkylcarbamoyl-methylphosphine oxide dissolved in tri-n-butyl phosphate on an inert support to selectively recover actinides.
U.S. Pat. Nos. 5,651,883 and 5,851,401, each to Horwitz et al., and Horwitz et al., Reactive and Functional Polymers, 33:25-36 (1997) teach the use of a diesterified methylenebisphosphonic acid extractant adsorbed on a solid support for the separation of trivalent, tetravalent and hexavalent actinide and lanthanide cations, as well as radium cations from aqueous solutions. The particularly preferred extractant of those patents is P,P′-bis(2-ethylhexyl)methylenebisphosphonic acid, that can also be named methylenebis(2-ethylhexyl hydrogen phosphonate), or H2DEH[MBP]. Methylenebis-(2-ethylhexyl hydrogen phosphonate) extractant is available commercially under the name Dipex® from Eichrom Technologies, Inc., of Darien, Ill.
Although particularly effective for removing those polyvalent cations, those bis-ester phosphonates are difficult and costly to prepare. For example, the synthesis of the preferred extractant, methylenebis(2-ethylhexyl hydrogen phosphonate), typically involves carbodiimide-promoted coupling of methylenebis(phosphonic acid) with 2-ethylhexanol in boiling tetrahydrofuran (THF) for several days, followed by extractions from ammonia solution and then acid solution. Chiarizia et al., Solvent Extr. Ion Exch., 14:773-792 (1996). This reaction is slow, and separation of the desired product from the other ester products requires a series of difficult extractions. In turn, these extractions generate large volumes of waste. This purification process makes large-scale synthesis of methylenebis(2-ethylhexyl hydrogen phosphonate) [Dipex®] laborious and costly to prepare.
It would therefore be advantageous if an easier and less costly, high yield synthesis could be provided. The disclosure below describes one such process.